Construction of the Core of Pseudolaric Acid A and Mechanistic Studies on Intramolecular [4+3] Cycloaddition

This paper describes the construction of hemiacetal 2, the core of pseudolaric acid A via oxidative cleavage of acetonide 6 or 7 and enolization-hemiacetalization of aldehyde 8. A plausible general mechanism for thc intramolecular [4+3] cycloaddition of sulfoxide 4 to adduct 3 is suggested.

Progress in organocatalytic asymmetric (4+3) cycloadditions for the enantioselective construction of seven-membered rings

Chiral seven-membered ring systems such as seven-membered carbocycles and heterocycles are widely found in natural products and pharmaceuticals.Therefore,the catalytic enantioselective construction of such frameworks has evoked considerable interest in the field of chemistry.Among the various approaches,organocatalytic asymmetric(4+3)cycloadditions are highly effective for the enantioselective construction of seven-membered rings.Over the past two decades,substantial efforts have been devoted to this field and chemists have developed various organocatalytic asymmetric(4+3)cycloadditions.This review summarizes the progress in organocatalytic asymmetric(4+3)cycloadditions from 2003 to early 2022 and provides insights into challenging issues faced in this research field,enabling the future development of this field.

Palladium-Catalyzed[4+4]Cycloaddition of Homo-TMM All-Carbon 1,4-Dipole Precursors for Construction of Benzofuro[3,2-b]azocines and Furo[3,2-b]azocines

We developed a novel Pd-catalyzed[4+4]cycloaddition of(benzo)furan-derived azadienes with homo-TMM all-carbon 1,4-dipoles in situ generated fromα-allyl malonate derivatives,affording an array of benzofuro[3,2-b]azocines and furo[3,2-b]azocines with good to excellent yields(up to 96%)and exclusive regioselectivities.This methodology featured mild reaction conditions and good functional group tolerance.The synthetic utility was demonstrated by a gram-scale reaction.Furthermore,the catalytic asymmetric[4+4]cycloaddition version has also been explored.

[4+3]Cycloaddition of ketenimines with furocarbenoids:Divergent and efficient synthesis of fused cycloheptatriene and tropone scaffolds

An unprecedent[4+3]cycloaddition of furoketenimines with furocarbenoids has been disclosed for the divergent and efficient synthesis of cycloheptafuran and cycloheptapyrrole scaffolds.Zinc chloride acted as promoters for both the formation of these two transient intermediates from isocyanides and ene-yne-ketones,and the subsequent construction of seven-membered ring.Three rings and five bonds were constructed successively in this three-component one-pot domino reaction.

Diastereodivergent formal[4+1]cycloaddition of azoalkenes as one-carbon synthons

The first diastereodivergent formal[4+1]cycloaddition reactions of azoalkenes with p-quinone methides(pQMs)have been accomplished.The reported reaction occurred via a domino oxa-1,4-addition/1,6-addition process,allowing the use of common azoalkenes as C1 synthons.A broad range of 2,3-dihydrobenzofurans was smoothly prepared in good yields and with reversible diastereoselectivities.The steric hindrance and hydrogenbonding interaction were proposed to account for the two different modes of diastereo-control.The projected reaction features the employment of azoalkene as carbene-like C1 synthon,mild conditions,broad substrate scope and tunable diastereoselectivity.

Elaboration of phosphoramidite ligands enabling palladium-catalyzed diastereo-and enantioselective all carbon [4+3]cycloaddition

A palladium-catalyzed diastereo-and enantioselective all carbon [4+3] cycloaddition of trimethylenemethane was developed by employing the elaborate tetrahydroquinoline-derived phosphoramidite ligand. The exclusive regioselectivity was realized by using the aromatization-driven diene indole-2,3-quinodimethanes, affording biologically important cyclohepta[b]indoles with excellent diastereo-, and enantioselectivities(up to >20:1 dr, >99% ee). Furthermore, the more challenging pyrrolidone-3,4-dienes, in the absence of aromatization force, were also compatible inthereaction, providing novel cyclohepta[c]pyrrol-1(2H)-ones with excellent regio-, diastereo-, and enantioselectivities(up to >20:1 rr, >20:1 dr, >99% ee).

Diastereo-and enantioselective palladium-catalyzed dearomative [4+2] cycloaddition of 3-nitroindoles

A Pd-catalyzed asymmetric decarboxylative[4+2]cycloaddition of 3-nitroindoles and vinyl benzoxazinanones is developed through a dearomatization approach.The reaction provides an efficient protocol for constructing a series of chiral tetrahydro-5H-indolo[2,3-b]quinolines in high yields and with excellent diastereo-and enantioselectivities.

Synthesis and thermal properties of novel calix[4]arene derivatives containing 1,2,3-triazole moiety via K_2CO_3-catalyzed 1,3-dipolar cycloaddition reaction

Two calix[4]arene derivatives containing 1,2,3-triazole moiety were synthesized via K2CO3-catalyzed1,3-dipolar cycloaddition reaction between calix[4]arene-based azide and active methylene compounds in good yields.The structures of the two compounds synthesized herein were fully confirmed by 1HNMR,,（13）C NMR,and MS（ESI）.The thermal analysis showed that the mass losses of the synthesized compounds 4 and 5 containing 1,2,3-triazole groups are similar to each other.

Intramolecular (4+3) cycloadditions of nitrogen-tethered epoxy enosilanes for the synthesis of heteropolycycles

Furans bearing epoxy enolsilane units via a tether that incorporates a nitrogen heteroatom,undergo intramolecular(4+3)cycloadditions to generate bis-heteroatomic polycyclic adducts having piperidine moieties in their frameworks.The cycloadducts,ultimately derived from furfural,a renewal chemical feedstock,are obtained with up to 4:1 dr and with ee retained from the epoxide.

One-pot synthesis of tetrahydroindoles via a copper catalyzed N-alkynation/[4+2] cycloaddition cascade

A CuSO_4 catalyzed ynamide formation/[4+2] cycloaddition relay reaction was achieved in one-pot.Various 4,7-cis-dihydroindolines were produced in good to high yields. The one-pot operation in conjunction with the cheap and benign copper catalysis renders this reaction highly sustainable.

Diastereoselective synthesis of spiro[chromane-3,30-indolines]and spiro[chromane-3,20-indenes]via DBU promoted formal[4+2]cycloaddition reaction

A new DBU-catalyzed formal[4+2]cycloaddition between ortho-hydroxyphenyl-substituted para-quinone methides and electron-deficient dienophiles including 3-methyleneoxindoles and 2-aryldeneindene-1,3-diones was established.A wide range of functionalized spiro[chromane-3,30-indolines]and spiro[chromane-3,20-indenes]were successfully synthesized in good yields and with high diastereoselectivity.The features of the reaction included readily available substrates,mild reaction conditions,convenient methodology and good functional group tolerance.

Lewis acid-catalyzed[4+2]cycloaddition of 3-alkyl-2-vinylindoles withβ,γ-unsaturatedα-ketoesters

A Lewis acid-catalyzed[4+2]cycloaddition of 3-alkyl-2-vinylindoles withβ,γ-unsaturatedα-ketoesters has been established in the presence of Sc(OTf)3,which afforded a series of indole-containing pyran derivatives in generally good yields(up to 90%yield)with excellent diastereoselectivities(up to >95:5 dr)under mild conditions.This approach not only enriches the chemistry of 3-alkyl-2-vinylindoles,but also has provided an atom-economic method for the synthesis of indole-containing pyran derivatives with potential bioactivity.

A Direct Route to Tetrahydropyridazine Derivatives via DMAP-Catalyzed [4+2] Annulation of Allenoates with Arylazosulfones

Herein,a DMAP-catalyzed[4+2]annulation ofα-substituted allenoates with arylazosulfones is reported,which affords facile access to tetrahydropyridazine derivative in synthetically useful yields.This reaction features mild conditions and good functional group tolerance.Moreover,the resultant products can be readily transformed into pyridazin-3-one derivatives in the presence of DDQ.

Palladium-catalyzed concerted [4+1] cyclization of prop-2-yn-1-ones and isocyanides

A palladium-catalyzed [4+1] cycloaddition of prop-2-yn-1-ones with double isocyanides is developed herein.The transformation worked well to produce a series of 2-amino-4-cyanofurans with high efficiency and a broad reaction scope.Based on mechanism studies,it is believed that the palladiumcatalyzed [4+1] imidoylative cycloaddition of prop-2-yn-1-ones was concerted.Treated with a ryl amine and H_2 O,the [4+1] cycloaddition of prop-2-yn-1-ones with double isocyanides provided 2-amino-4-amidylpyrroles efficiently.

Reaction of o-Carboryne with Furans： Facile Synthesis of Carborane- Fused Oxanorbornenes and Their Derivatives

o-Carboryne （1,2-dehydro-o-carborane） is a very useful synthon for the synthesis of a variety of carborane-functionalized molecules. Diels-Alder reaction of o-carboryne with furans gave a series of carborane-fused oxanorbornenes in moderate to high yields using 1-OTf-1,2-C_2B_10H_11 as carboryne precursor. The resultant cycloadducts can undergo hydrogenation, cyclic oxidation, bromination, [4＋2]/[2＋2] cycloaddition and nucleophilic ring opening reaction to afford a variety of highly functionalized carboranes that may find applications as useful basic units in medicine and materials science.